1. Technical Field
The invention relates to drain plugs and in particular to a drain plug for venting and relieving residual pressure in a pressurized system while a sufficient number of threads on the plug remain engaged to prevent the premature release of excess residual pressure or possible blow out of the plug to prevent injury to an operator.
2. Background Information
Various types of pressure systems such as those containing hydraulic fluids, hazardous liquids including radioactive liquids, expensive liquids and gases, as well as various high pressure gasses, steam and the like are provided with drain plugs for removing gas or liquid from the system for a variety of reasons.
Occasionally an injury to an operator can occur or the expensive liquid or gas can be lost should an operator remove the drain plug while residual pressure remains within the pressurized system. Occasionally the operator will begin to unscrew the drain plug from its threaded opening and upon nearing the end of the threaded shank, the residual pressure will "blow out" the drain plug, possibly striking the operator or causing injury as well as spraying various high temperature or toxic chemicals upon the operator or into the surrounding atmosphere.
Thus, the need exists for a drain plug which can be installed in a pressurized system which will ensure that the operator becomes aware of any residual pressure remaining in the system should he or she begin to unscrew the drain plug while such residual pressure remains in the system while sufficient threads of the drain plug are engaged within the threaded opening to prevent premature ejection or "blow out" of the plug.
Various types of check and relief valves have been devised in order to reduce or eliminate this problem. However, most of these valves are provided with some type of spring biased ball or detente member which upon movement of certain components of the valve, will bleed or vent gasses or liquids from various gauges, instruments, pressurized containers or the like. These devices will assist in preventing the accidental removal of the drain plug or check valve while sufficient pressurized gas or liquid remains in the system which could possibly injure the operator. Although these check and relief valves or purge valves provide a solution to the problem, they consist of several components which are always subject to maintenance and repair and are more expensive than desirable. Also they occupy additional space than a usual drain plug which can be a problem in certain pressurized systems where space is at a premium.
My invention provides for the safety of the operator by a very inexpensive drain plug which is free of any moveable parts and requires only the formation of a hole or groove throughout the threaded shank portion of the plug, and which provides for the partial venting of the pressurized fluid upon partial unloosening of the drain plug.